Microwaves cover waves at frequencies lying in the range 0.3 GHz to 300 GHz, and more particularly lying in the 0.3 GHz to 5.2 GHz band.
The forwards direction is defined as being the direction in which the wave propagates in the cavity. Consequently, the front wall of the feed waveguide is defined as the wall which, in the propagation direction, lies downstream, whereas the rear wall is the wall which, in the same direction is upstream.
European patent application EP-A-0 446 114 discloses a device designed for microwave treatment of sheet or foil products in which openings for passing the product are provided in the form of thin slots, and the walls of the feed waveguide are perpendicular to the longitudinal direction of the waveguide cavity.
To deflect the propagation direction of the wave leaving the feed waveguide, there are provided two guide flaps inclined at 45.degree., together with trapping plates. The two flaps are spaced apart at a very small distance so as to provide almost continuous guidance for the wave, such that it is possible to pass only a product that is in foil or sheet form.
A product in foil or sheet form is a product which has very small size in one of the directions extending transversely to its longitudinal direction.
The term "elongate product" is used herein in general to designate any product of generally uniform section but of arbitrary transverse dimensions. This definition covers elongate products both of whose transverse directions are comparable, such as section bars, or even cylinders or tubes.
Known devices do not enable such elongate products to be treated with an electric field extending perpendicularly to the longitudinal direction because the transverse dimensions of the product are too large to enable it to pass through the thin slots and between the above-mentioned flaps.